hammer out - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Work out with considerable effort, as in It took weeks of negotiations to hammer out an acceptable compromise. This usage likens intellectual effort to shaping metal with the blows of a hammer. [Mid-1700s]